This invention relates to devices and methods for sequential fractionation and extract of elements from complex solid samples. More particularly, this invention relates to a sequential processing reaction vessel and method for accelerated fractionation and extraction of analytes from solid samples which is compatible with microwave heating sources and which reduces processing time and transfer losses, improves extraction efficiency, and provides for accurate total analysis of solid samples.
Sequential extraction methods have been previously developed to address specific questions to enhance understanding of elemental behavior in complex oceanographic and geological samples [see R. Chester et al., Chemical Geology, 2: 249-262 (1967); A. Tessler et al., Analytical Chemistry, 51(7): 844-850 (1979); D. W. Eggimann et al., Jour. Sediment Petrol. 50: 215-225 (1980); J. M. Robbins et al., xe2x80x9cA Sequential Extraction Procedure for partitioning elements among co-existing phases in marine sedimentsxe2x80x9d, College of Oceanography, Oregon State University, Ref.#84-3, 64pp. (1984); S. B. Moran et al., Geochimica Cosmochimica Acta, 55: 2745-2751 (1991); and R. Chester et al., Journal of the Geological Society, London, 151: 351-360 (1994)].
Analytical techniques most commonly used for the chemical fractionation of Si in biogenic and lithogenic sedimentary particles are based on the higher solubility of biogenic silica in alkaline solutions at elevated temperature and pressure. Several variations of this technique require pretreatment of the sample, heating of the sample in the presence of an alkaline solution and the separation of the solution from the remaining particles [see D. W. Eggimann et al., Jour. Sediment Petrol. 50: 215-225 (1980); P. J. Muller et al., Deep-sea Research, Vol. 40, No. 3. Pp. 425-444 (1993); D. J. DeMaster, Geophysical Monograph 63: 363-367 (1991); and R. A. Mortlock et al., Deep-sea Research, Vol. 36, No. 9, pp. 1415-1426, (1989)].
Methods have been developed for the fractional analysis of marine sediment samples where the elements Ca, Mg, and Sr are associated with the biogenic carbonate fraction and lithogenic fraction [see M. Bender et al., Micropaleontology, vol. 21, no. 4, pp.448-459 (1975); and S. R. Taylor, Geochimica et Cosmochimica Acta, Vol. 28 pp.1273-1285 (1964)].
The separation of various chemical fractions of phosphorus is of particular interest to biogeochemical researchers [see K. C. Ruttenberg, Limnol. Oceanogr., 37(7), pp. 1460-1482 (1992)]. While fractionation methods have been developed for determining particulate phosphorus found in the water soluble and acid-soluble portion of ocean particles [see G. Liebezeit, Marine Chemistry, 33: 61-69 (1991)], the lithogenic P fraction has not yet been precisely characterized by existing methods.
The elements Al, Ti, and Fe that are primarily associated with the lithogenic component of ocean particles have a small but very significant fraction associated with biogenic material and adsorbed/scavenged elements. These fractions have been accessed by several chemical treatments [see K. W. Bruland et al., Geochimica Cosmochimica Acta, 58: 3171-3182 (1994); R. W. Murray et al., Paleoceanography, Vol. 8, No. 5, pp. 651-670 (1993); and S. B. Moran et al., Geochimica Cosmochimica Acta, 55: 2745-2751 (1991)].
The current methods and reaction vessels for extracting elemental constituents from complex solid samples typically involve tedious, multi-stage solution treatments where solid samples must be repeatedly removed, weighed, dried and transferred between successive reaction vessels for extraction and fractionation analysis of individual constituents. Due to repeated sample losses and contamination introduced during multiple sample transfers, such methods generally suffer from a lack of reproducibility, precision and accuracy. Due to the number of treatments and sample transfers typically required, such methods are intrinsically inefficient and due to the considerable sample preparation and transfer times.
It is anticipated that a method which could overcome the limitation of existing fractionation methods and substantially reduce sample transfers, preparation times and costs would be particularly beneficial to the analysis of solid samples in a variety of industrial, environmental and research applications.
The sequential processing reaction vessel (SPRV) device and method of the present invention provide for accelerated sequential processing of solid samples at high temperatures and pressures within a single reaction vessel. The method employs a series of reagent solution treatments introduced in a microwave transparent, flow-through reaction vessel that retains the solid samples on a membrane filter and frit while permitting introduction and removal of a variety of sample treatment solutions for extraction and fractionation analysis of target analytes.
The SPRV reactor is preferably fabricated with a microwave transparent polytetrafluoroethylene (PTFE) inner vessel and a polyetherimide (sold under the trademark ULTEM(copyright)) outer vessel which permit microwave heating of the reactor for accelerated analyte extraction and sample digestion at temperatures up to 150xc2x0 and pressures up to 150 psi.
The reactor of the present invention provides for rapid sample addition and removal by providing for partial assembly of the reactor housing with retention of a sample membrane filter which facilitates charging of the reactor with solid samples prior to sequential processing solution treatments and eliminates sample transfer losses and contamination during addition of solids to the reactor. A variety of reagent solutions may be sequentially introduced and removed from the innovative reactor of the present invention without disassembly or removal of the solid samples.
During operation of the device of the present invention, pressure can be introduced into the top cover opening to force liquid to pass out the bottom opening. This is an important feature which permits automation of the flow-through system and allows the vessel and sample to remain in the an oven while liquids can be programmed to flow in and out of the vessel. Additional auxiliary openings in the top cover permit the monitoring of reactor temperature and pressure during operation.
The device of the present invention further provides for an innovative laminated membrane filter for retention of solid samples during sequential processing treatment. The use of the innovative laminated filter provides for improved mechanical durability of the membrane when operating at high liquid pressures, eliminates liquid flow by-pass and leakage around the membrane, and maintains high solids retention while permitting pressurized fluid flow through the membrane when discharging reagent liquids at the end of treatment cycles.
The device and method of the present invention provide for efficient accelerated sequential processing of solid samples with a variety of reagent solutions for rapid, low cost fractionation analysis of solid materials with high analytical reproducibility, precision and accuracy and minimum sample losses or contamination due to unnecessary sample transfers.